Chalcogenide Perovskite Thin Films by Ultrasonic Spray Pyrolysis

Perovskite materials are currently a focal point of research in optoelectronics, including fields such as photodetection and solar energy utilization. Compared to the widely used halide perovskites, chalcogenide perovskites—distinguished by their excellent structural stability and unique optoelectronic properties—have emerged as promising new semiconductor materials. They hold the potential to overcome the performance limitations of traditional optoelectronic materials and are suitable for full-spectrum detection scenarios spanning ultraviolet, visible, and near-infrared ranges.

Chalcogenide perovskites feature the classic ABX₃ perovskite crystal structure, offering both structural stability and tunable optoelectronic properties. Their crystal structure is formed by corner-sharing octahedral units with metal cations occupying the interstitial sites; this unique configuration provides an excellent structural foundation for charge transport. Taking zirconium-based sulfide perovskites as an example, the atomic chemical bonds within the material exhibit significant covalent character. Orbital hybridization effects lead to greater band-edge dispersion, resulting in lower carrier effective masses and significantly enhanced carrier mobility. Furthermore, the dense distribution of orbital energy levels grants the material exceptional band-edge light absorption capabilities, perfectly meeting the critical requirement for high light-harvesting efficiency in optoelectronic devices, making them ideal functional optoelectronic materials.

Despite their outstanding performance, the industrial application of chalcogenide perovskites has been severely constrained by traditional fabrication techniques. Current mainstream processes largely rely on high-temperature solid-state synthesis, which requires temperatures exceeding 900°C and involves extremely time-consuming sulfurization steps. Physical fabrication methods—such as laser sputtering and molecular beam epitaxy—entail high equipment costs and complex processes, while also making the monolithic integration of thin films and devices difficult. Although subsequently developed solution-based synthesis methods have lowered some barriers, they involve cumbersome steps and lengthy cycles, and are prone to generating structural defects and impurity phases, making it challenging to produce high-quality, highly stable thin-film materials.

To address these technical challenges, the industry continues to explore low-cost, high-efficiency fabrication solutions. Research indicates that tin-based and zirconium-based chalcogenide perovskites possess ideal bandgap ranges for optoelectronic applications, exhibit extremely low effective masses for both electrons and holes, and demonstrate outstanding carrier transport performance. The bond strength characteristics of Sn-S octahedra optimize the valence band structure and suppress the negative effects of polarons, thereby further enhancing hole mobility and offering the dual advantages of broad-spectrum absorption and efficient charge carrier transport. However, the industry has long lacked a simple solution-based process for the direct fabrication of multi-component Ba-Zr-Sn sulfide perovskite thin films.

To address this, a novel ultrasonic spray pyrolysis technique has been developed, successfully enabling the direct fabrication of non-stoichiometric Ba-Sn-Zr sulfide perovskite thin films. This technique utilizes conventional chemical reagents to prepare a single, homogeneous precursor solution; the precursor layer is deposited via ultrasonic spraying and followed by rapid thermal processing. This approach significantly simplifies the fabrication process and shortens production cycles, overcoming the drawbacks of traditional methods—namely high temperatures, complexity, and high costs.

Structural characterization reveals that the new thin film is a composite of multiple stable crystalline phases. It is dominated by distorted orthorhombic Zr-based and Sn-based sulfide perovskite phases, supplemented by minor secondary sulfide phases, resulting in a stable crystal structure with low defect density. Optical testing indicates a near-ideal bandgap of 1.46 eV; the film exhibits excellent light absorption in the ultraviolet and visible ranges, as well as significant sub-bandgap absorption in the near-infrared range, demonstrating an exceptionally broad spectral response.

The multi-component sulfide perovskite thin film demonstrates outstanding optoelectronic response characteristics. It produces stable optoelectronic signals that are minimally affected by the wavelength of incident light, enabling stable detection across the full ultraviolet-visible-near-infrared spectrum. Furthermore, it exhibits excellent cycling stability, showing no significant performance degradation under prolonged, repeated illumination.

This research overcomes the technical barriers associated with traditional sulfide perovskite thin-film fabrication, achieving high-performance composite-phase perovskite films through a low-cost, simple, and controllable solution process. With advantages such as broad spectral response, high stability, and an optimal optical bandgap, this novel thin-film material holds great promise for applications in photodetectors, optical sensing, and clean energy, while also offering a new paradigm for the design and large-scale fabrication of high-performance sulfide perovskite optoelectronic materials.

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